Method and apparatus for heating metal pipe or the like



June 30, 1942. PRAY 2,288,483

METHOD AND APPARATUS FOR HEATING METAL PIPE OR THE LII/IT- Filed Oct. 23, 1940 INVENTOR f/en 13' A b. Pray Patented June 30, 1942 METHOD AND APPARATUS FOR HEATING METAL PIPE OR THE LIKE Henry A. H. Pray, Columbus, Ohio, assignor, by mesne assignments, to The Youngstown Sheet and Tube Company, Youngstown, Ohio, a corporation of Ohio Application October 23, 1940, Serial No. 362,368

Claims.

This invention relates to a method and apparatus for heating elongated articles such as pipe, rods or the like.

In certain processes, it is desirable to heat elongated articles such as pipe or rods to a specifled temperature, without substantial variation thereof along the length of the articles. One such application is the baking of a'synthetic resin lacquer on a pipe, for example, to protect the surface against corrosion; In this process, uniformity of temperature along the length of the pipe is of extreme importance. In fact, temperature differences of more than about F. are objectionable.

The heating of articles composed of electrically conducting materials, by passing a heating current therethrough is desirable for numerous reasons. When it has been attempted to heat elongated articles such as pipe or rods by this method, however, it is observed that substantial differences exist between the temperatures of various points along the length of the article. Such variations seem to depend on conditionsat the area of contact between the article and the electrodes through which the heating current is supplied. Ifpthe contact resistance is high, the portion of the article adjacent the electrode becomes overheated. If the contact resistance is low, the portion of the article adjacent the electrode is cooled by conduction through the electrodes and current leads.

I have invented a novel method and apparatus for heating elongated articles such as pipe or rods, by their electrical resistance, whereby the article is heated to a temperature which is substantially uniform throughout its entire length.

I thus avoid the loss involved in scrapping the ends of elongated articles as would otherwise be necessary because of improper heating, i. e., to a temperature above or below that desired for the best result. In a preferred practice of the invention, I supply current to the article through terminals having a shape and cross sectional area similar to that of the articles themselves. I proportion the terminals so that they constitute a thermal reservoir of substantial capacity, in order to avoid loss of heat from the articles by conduction through the terminals and the electrical leads. I also mount the terminals so that the ends thereof abutting the arti cle are subjected to about the same cooling effect as the latter. As a result, current flow through the terminals and the article causes the latter and the inner ends of the terminals to heat up same temperature as the body of the pipe under treatment. As an aid to this end, I may utilize conducting gaskets of a material softer than that of which the terminals and the articles are composed, disposing the gaskets between the termi- I nals and the article and applying pressure there-,

to suflicient to deform the gaskets into intimate contact with the terminals and the article.

While the invention may be practiced with a variety of different forms of apparatus, I have disclosed herein one embodiment comprising a supporting table or bench having spaced terminal supports thereon, one of which is adjustable longitudinally but is normally fixed. The other is movable toward and from the relatively fixed support and I provide means such'as a fluidpressure cylinder and piston for actuating the movable support into engagement with the article being treated, when the latter has been properly positioned between the terminals.

The preferred embodiment and practice of the invention are illustrated in or will be explained in connection with the accompanying drawing showing the apparatus. In the drawing:

Fig. 1 is a longitudinal, vertical, central, sectional view through the apparatus with parts in elevation; Fig. 2 is a similar view showing a modified form of terminal apart from its support; and

Fig. 3 is a curve showing the variation oftem-.

perature throughout'the lengths of the terminals and the article.

Referring now in detail to the drawing, the apparatus shown is adapted particularly for and the method will be explained in connection with the treatment of pipe or tubes such as that indicated at In. It will be understood, however, that the invention is also applicable to the treatment of various other forms of elongated articles composed of electrically conducting material. The apparatus for receiving the pipe l0 during treatment comprises a bench or supporting frame ll having ways 12 extending therealong. A terminal support l3 is'slidable on the ways l2 and is provided with a pillow block and securing cap for mounting a terminal l4 thereon. A sleeve .the support I3. A lug I6 is welded to the outer end of the terminal H and is provided with a binding screw for the attachment of a currentsupply lead I! thereto. V

, A screw shaft I 8 is journaled in bearings l9 and 20 in the bench or frame II. The shaft is threaded through a nut 2| disposed between bifurcated lugs 22 depending from the support l3.

The latter may thus be adjusted along the ways [2 by turning the screw shaft l8. When adjusted to the proper position, the support I3 is secured to the bench by clamping bolts 23.

A terminal support 24 is movable longitudi-- nally of the bench H to a limited extent. It is provided with a terminal 25 in an insulating sleeve 26 and is similar. in general to the terminal l4 and its support N. A cylinder 21 mounted on the bench ll adjacent the support 24 has a piston 28 reciprocable therein adapted to engage a bearing pad 29 on the lug it of the terminal 25. It will be apparent from the foregoing description that when a pipe I is disposed between the terminals l4 and 25 after adjustment of the terminal l4 and retraction of the terminal 25, the cylinder 21 and piston 28 may be operated to force the terminal 25 against the end of the pipe I I0, thereby exerting the desired contact pressure thereon.

As an aid to positioning the pipe lll properly for engagement by the terminals l4 and 25, I

provide a split V-block 30 on the bench H, the v two halves of which may be separated or brought together by a screw shaft 3| having oppositelythreaded portions cooperating with threaded bores in the lower portions of the-halves of the block 30. A hand wheel 32 on one end of the shaft 3| permits the halves of the V-block to be brought together or separated to the extent necessary to support the pipe III at the proper elevation and in alinement with the terminals I4 and 25.

In carrying out the method of my invention, I dispose a pipe I0 between the electrodes l4 and 25 and cause the terminals to exert such pressure on the article that on circulation of current through the terminals and article in series,

the abutting portions of the terminals and pipe will be heated to about the same temperature as the body portion of the pipe. This requires that the resistance of the contacting areas of the pipe and terminals be reduced to a minimum. While this can be accomplished by carefully machining the ends of the terminals and pipe and by using sufllcient contact pressure, an easier method of insuring the desired minimum contact resistance between the terminals and pipe is to insert electrically conducting gaskets therebetween composed of a metal softer than the pipe and terminals and capable of suflicient deformation under pressure to insure a low-resistance contact with the pipe and terminals despite minor irregularities in the machining of the ends thereof. If steel pipe is being processed, the gaskets 33 may conveniently be of copper.

It will be observed that the terminals l4 and 25 project inwardly for a considerable distance beyond their supports. This assures that the portions of the terminals nearest the pipe are .per unit of length, and since the cooling eiiect to which the inner ends of the terminals are sub that shown at 25,

' terminals and pipe in series, the pipe jected is the same as that which exists in respect to the pipe l0, it will be apparent that the inner ends of the terminais'and the pipe [0 will be heated to the same temperature by the passage therethrough of a given amount of current for a predetermined time.

The terminals i4 and 25, furthermore, are long enough to constitute a thermal reservoir of substantial capacity, so that only a limited amount of heat is conducted therefrom through the connecting lugs Hi and leads IT. The insulating sleeves l5 and 26 prevent substantial loss of heat'by conduction to the terminal supports l3 and 24.

As a result of the several factors mentioned above, the curve of temperatures at various points along the combined lengths of the terminals and electrodes is as illustrated in Fig. 3. As clearly shown there, the temperature curve is a horizontalline throughout the length of the pipe l0 and the greater portion of the lengths of the terminal [4 and 25. Adjacent the outer ends of the latter, the temperature falls because of the conduction of heat therefrom through the electrical connections. The absence of peaks in the temperature curve opposite the gaskets 33 indicates that the contact resistance between the terminals and the pipe is not materially dif-- ferent from the resistance of the terminals or the pipe themselves. The existence of excessive contact resistance would be revealed by temperature peaks such as those indicated in dotted lines at 34 but such peaks are substantially eliminated by the practice of the invention.

In a specificinstance, a 2" placed between the terminals I4 contact pressure of 1500 pounds (total), with the gaskets 33 of A;" thick, dead-soft copper between the terminals and the pipe. On circulating a current of 2000 amperes through the was heated to a temperature of about 360 F. in about three and a half minutes. While alternating current was used for convenience, direct current may be used just as well.

Fig. 2 illustrates a modification of the structure and procedure described above. As there illustrated, a terminal 25', similar in general to has a gasket ring 33' similar to those shown at 33 brazed thereto. This ring further reduces contactresistance between the terminal and the pipe.

The gaskets must be clean and flat and the ends of the terminals and square although, as above stated, minor irregularities are not fatal because the gaskets are soft enough to be deformed so they will accommodate themselves to such irregularities. In order to prevent tarnishing of the gaskets, they may be plated with a soft metal of high conductivity such as silver. Special provisions may be made for artificial cooling of the terminals by streams of air or water after each heating operation, in order to bring them quickly down to the temperature of the cold pipe next to be treated.

The apparatus shown, as stated, is particularly ste l pipe was and 25 under a and pipe should beflat useful in the process of baking a resin-lacquer coating on metal pipe. This coating sufficiently insulates the pipe from the supporting V-block 30. In other processes, suitable insulation may be applied to the surfaces of the block which engage the pipe, if necessary.

The length of the pipe being processed may vary between wide limits. With longer lengths of pipe, of course, the applied voltage must be increased to obtain the desired heat in the same length of time. In processing larger sized pipe, the pressure applied must be increased proportionally. It is not necessary, however, to increase the length of the terminals if the heating current is increased to maintain about the same rate of heating.

It will be apparent from the foregoing description and explanation that the invention provides a simple and convenient method and apparatus for processing pipe or the like in such manner that all portions of the length thereof will be subjected to the same treatment. I thus avoid the necessity for scrapping the ends of the pipe which is necessary when a substantial difference exists between the temperatures at the ends of the pipe and throughout; the remainder of the length thereof.

Although I have illustrated and described but a preferred embodiment and practice of the invention, it will be recognized that changes in the structure and procedure disclosed may be made without departing from the spirit of the invention or the scope of the appended claims.

I claim:

1. In a method of heating elongated metal articles to a substantially uniform temperature throughout the entire length thereof, the steps including disposing an article between and in endwise, electrically-conducting abutment with terminals having a shape, cross-sectional area, and resistance-heating characteristics substantially identical to those of the article, and passing electric current through the terminals and the article in series in the absence of artificial cooling, whereby to heat the terminals to substantially the same temperature as said article, while exerting sufficient contact pressure at the joints between the terminals and the article to prevent them from being heated to a temperature materially higher than the temperature of said article.

2. A method of heating as defined by claim 1 characterized by disposing electrically conducting gaskets between said terminals and the article, composed of material deformable under said contact pressure.

3. In a method of heating elongated metal articles to "a substantially uniform temperature throughout the entire length theroef, the steps including disposing an article between and in endwise, electrically-conducting abutment with terminals having a shape, cross-sectional area,

.and resistance-heating characteristics substantially identical to those of the article, placing gaskets of electrically-conducting material between the terminals and the ends of the article and passing electric current through the terminals, gaskets and article in series, to heat the terminals and said article to substantially the same temperature, while exerting sufficient contact pressure at the joints between the terminals and the gaskets and the gaskets and the article to prevent them from being heated to a temperature materially higher than the temperature of said article.

4. Apparatus for heating elongated metal articles having substantially the same cross-sectional area throughout their length, to substantially the same temperature at all points, comprising a pair of elongated, spaced terminals adapted to engage the articles,'and of substantially the same cross sectional area for a substantial distance from the engaging ends, whereby said terminals are heated to the same temperature as the article for a substantial distance from the engaging ends, the ends of the terminals being shaped to be fully seated on the ends of the articles without any portions of the ends of the articles extending beyond the seated portions of the terminals, and means for moving one terminal towards the other to place all portions of the ends of the articles and all portions of the ends of the terminals under pressure.

5. Apparatus for heating as defined by claim 4 characterized by means for mounting said terminals eifective to prevent loss of heat from the ends thereof adjacent the ends of the article, at a rate substantially greater than that at which the article itself loses heat.

HENRY A. H.- PRAY. 

